Do black holes always rotate in the same direction ?

[Aunt Maud]

I ask this question today, because I'm wondering what would happen if two black holes rotating in opposite directions were to collide ?

[ian]

Space is three dimensional. The direction in which a black hole rotates is determined by where you are relative to the black hole. Black holes can rotate either way relative to each other, the rotation comes from the spin of the matter of that created them. It's a bit of head-scratcher tbh how black holes come to be colliding in the first place, but it's likely they came from closed aligned stars in which case you'd intuitively expect them to be spin-aligned. The collisions LIGO has detected so far do seem to be axially misaligned which throws a bit of a spanner in the works. I don't think anyone has ever seen two completely counter-rotating black holes collide. Well, no one human anyway. I'm not clever enough to know how much all that angular momentum would add to the already heady mix.

I'd imagine tidying up afterwards would be even worse than after a teenager's house party that got advertised on Facebook.

[zendog]

No - they rotate in the direction of the net angular momentum of the part of the gas cloud they formed from. The galaxy has a direction of rotation
but interstellar gas clouds have complex origins and inside a cloud or in two clouds rotation could be either way.

The total energy of colliding black holes is HUGH if not bigger.  Spin is part of this but not dependent on direction spin. I get the feeling
this has been computer modelled and it ends up with a bigger black hole and a shed full of radiation. Try Google?

Not astrophysicist but interested. 

[BrianI]

An interesting conundrum.

Whatever you do though, don't fall into a black hole, with a pet robot called Maximillian!

 https://www.youtube.com/watch?v=nFv9ZRAqG1s

 

Sadly, Disney don't make films like this anymore! (Disney's The Black Hole)

[sojournermike]

An interesting conundrum.

Whatever you do though, don't fall into a black hole, with a pet robot called Maximillian!

 https://www.youtube.com/watch?v=nFv9ZRAqG1s

 

Sadly, Disney don't make films like this anymore! (Disney's The Black Hole)

Should be ok if it's spinning;)

[Aunt Maud]

Well, this is moving along nicely.

If I could simplify it a little. I was really wondering; if they didn't rotate in the same direction relative to where I was standing but were axially aligned and say the ones rotating clockwise were sucking from the side I was standing, like a bath plughole in the northern hemisphere. And the ones that were rotating counterclockwise were blowing.

Would they just cancel each other out and disappear ?

[ian]

Water going down the plug hole actually doesn't vary between hemispheres, the coriolis effect isn't strong enough to overcome the effect of gravity, friction and fluid turbulence (it does determine the spin of hurricanes and cyclones though).

But anyway, no. All that angular momentum has to go somewhere, so even if we put gravity aside, the results are still going to be, erm, a tad energetic.

[zendog]

All black holes have already "disappeared" behind their event horizons. That's the black bit - you cannot see them.

Mass / energy cannot cancel - it's all just energy. You just get a bigger black hole which you still cannot see!
It's rotational energy will be the net of the two originals so in the extremely unlikely event of exactly equal /oposite
angular momentums you would be left with a non rotating black hole.

[Aunt Maud]

But if you went and looked at it from the other side it'd be full of stuff.

[zendog]

OK you got me.

But it was an interesting think for a while on a lazy Wednesday.

Cheers

Steve
 

[LEE]

It's like asking which way the Earth rotates surely.  It rotates in space and space provides you with an infinite number of viewpoints on that rotation.

Black Holes, and their child Galaxies, rotate in space in the same way, for the same reasons as far as I can tell. 

Also...all the talk of portals to a different dimension puzzle me.  I though that, at the heart of a black hole , it was basically a lump of very hard, compressed, stuff.  The "hole" is just an expression that describes the fact that you can't see the hard lump (that you would become a very tiny part of)

[zendog]

My late respected maths teacher said "anyone who uses surely in an augment is never sure and usually wrong".

It works nearly every time. Check out the letters page of the daily wail for lots of examples.

No offence obviously.

[LEE]

My late respected maths teacher said "anyone who uses surely in an augment is never sure and usually wrong".

It works nearly every time. Check out the letters page of the daily wail for lots of examples.

No offence obviously.

Sounds like your Maths teacher was a smug Cunt. Definitely.

Edit.  "Check out the letters page of the daily wail ." No.  Who would do that?

[Kim]

It's like asking which way the Earth rotates surely.  It rotates in space and space provides you with an infinite number of viewpoints on that rotation.

The Earth comes with a convenient solar system (or even galaxy) full of reasonable reference points, of course.  Not that it didn't take the BBC graphics department a week or two after the launch of The Day Today News 24 to decide which way it goes...

[Basil]

This is the sort of thread that has been missing from yacf for ages. 

Hoorah

[Efrogwr]

One of my friends is a physicist and an ace mathematician. She's just pressented an art installation called "the Dark Heart of Cepheus" which deals with the biggest known black hole. I'll ask her wnen Inext see her.

[Jaded]

Aren't black holes Brilliant!

[ian]

Also...all the talk of portals to a different dimension puzzle me.  I though that, at the heart of a black hole , it was basically a lump of very hard, compressed, stuff.  The "hole" is just an expression that describes the fact that you can't see the hard lump (that you would become a very tiny part of)

That's the problem, you can't say what's in a black hole because the physics to describe it breaks down. Classical relativity has an infinitely dense mass, but no one knows what that is, and physics generally abhors infinities. Loop quantum gravity gets around that by quantizing spacetime itself so there can't be an infinity (and it provides a handy explanation for Hawking radiation). That said, despite it's elegance, I don't think there any experimental evidence for loop yet. It's not like I can do the math. I can't even do long division. Einstein was crap at maths too, but I think crap in this context is relative. I feel sure he'd be able to do long division, for instance. String theory was always too complicated and took a bump when no supersymmetric particles turned up at the LHC party despite our sending out lots of invites. The most amazing and puzzling thing about LHC is what we haven't found.

I can't get my head around dark matter. I've checked all my cupboards and wardrobes and I can't find it either. I found a lot of shoes though.

[Aunt Maud]

Aren't black holes Brilliant!

No, I would imagine they were quite dark.

[mattc]

If we sent a million left-handed M6 screws into space, then however far they travel, or how much they spin/tumble, they won't become right-handed.

[I don't actually think black-holes all have the same "handedness", but it's not a ridiculous idea; the laws of electromagnetism are "handed". ]

[Asterix, the former Gaul.]

This is the sort of thread that has been missing from yacf for ages. 

Hoorah

Yes, it demonstrates that escaping from a black hole is in fact possible.  It could even demonstrate the existence of Hawking Radiation.

Aren't black holes Brilliant!

No, I would imagine they were quite dark.

It's possible they are only dark from the outside.  After all if all light disappears into them and can't get out then they could be quite dazzling inside.  We need a volunteer to go in and report back.  They'll need good sunglasses..

[ian]

Our entire universe could be in a black hole. Which, I suspect, may explain Swindon.

[Asterix, the former Gaul.]

I ask this question today, because I'm wondering what would happen if two black holes rotating in opposite directions were to collide ?

A collision would be impossible because they could only rotate in opposite directions whilst in different hemispheres.  Like bathwater.  Obviously bathwater going down the plug couldn't collide because it would be in two different baths.

[Ben T]

What I don't get about black holes, is if they have infinite mass, why don't they have infinitely dense gravity - and suck everything in no matter how far it is away? At infinite speed?
Either they don't have infinite mass/gravity, or they (or one) actually has already sucked us in.

[ian]

Gravity is a force and follows the inverse square law (and weakens by the square of the distance – exactly the same as other forces). There's no such thing as 'infinite gravity' or, for more arguably, 'infinite mass' (the latter is why we can't to say what's in a black hole, what is 'infinite mass' in reality). And theories like loop quantum gravity do away with those pesky infinities.